1. Field of the Invention
The present invention relates to a sound field control method and a sound field control system for obtaining reproduction sound with full realism by adding predetermined reverberation to the reproduction sound in sound reproduction in a reproduction sound field.
2. Description of the Related Art
Conventionally, propositions of methods or systems for obtaining sound with full realism in the case of reproducing and listening to music have been made. As one of the propositions, there is a system called a trans-aural system. This trans-aural system is a system for attempting to obtain realism similar to that of the case listening in target sound space by listening to sound recorded in both of ear portions of a dummy head placed in a position corresponding to a position of a listener in target sound space in a reproduction sound field.
This provides sound information similar to that on a recorded sound field for a listener by matching sound pressures PL, PR of respective external auditory meatus entrances of both of right and left ears of the dummy head in the case of recording with sound pressures SL, SR of respective external auditory meatus entrances of both of right and left ears of the listener in the reproduction sound field. In order to achieve such a reproduction state, there is provided a reproduction equivalent filter called a crosstalk cancel filter and control of the reproduction sound field is performed.
Also, as a method for obtaining sound with full realism similarly, there is a signal processing apparatus called a reverberation addition apparatus. Generally, this has an initial reflected sound generation part with a finite length in a front stage of a system and adds its output signal to a reproduction sound source in a reverberation generation part of a backstage. A form in which filters of IIR (Infinite Impulse Response) type like a comb filter are arranged in parallel is generally used as the reverberation generation part. Further, in addition to these, a form in which an impulse response of an actual sound field is convolved with the reproduction sound source has also been proposed.
However, in the conventional trans-aural system, a purpose is to strictly control localization, reverberation and sound quality of an original sound field, so that an optimal solution of a filter for canceling characteristics of the reproduction sound field did not necessarily become stable and also when there is a big difference between characteristics of the original sound field and the reproduction sound field, an uncomfortable feeling might remain acoustically. Also, by strictly obtaining characteristics in both of right and left ear positions, realism in the original sound field can be obtained in the case of listening in an optimal position, but even in the case of listening in a position slightly deviating from its point, it became realism quite different from that in the original sound field and a narrow control area became a problem.
Also, in the conventional reverberation addition apparatus, sound addition information, that is, phase, amplitude, reverberation characteristics, etc. were determined and provided uniquely based on know-how of a designer without consideration of characteristics of the reproduction sound field. Because of that, the addition information did not always match with each the reproduction sound field, and also in a form in which sound field data of the reproduction sound field is convolved directly with the reproduction sound source, a long filter was required and it became a large-scale system configuration.